52nd Lunar and Planetary Science Conference 2021 (LPI Contrib. No. 2548) 2740.pdf THE CHAIN OF ROOTLESS CONES IN CHRYSE PLANITIA ON MARS. L. Czechowski1, N. Zalewska2, A. Zambrowska2, M. Ciążela3, P. Witek4, J. Kotlarz5, 1University of Warsaw, Faculty of Physics, Institute of Geophysics, ul. Pasteura 5, 02-093 Warszawa, Poland, [email protected], tel. +48 22 55 32 003, 2Space Research Center PAS, ul. Bartycka 18 A, 00-716 Warszawa, Poland, 3Space Research Center PAS, ul. Bartycka 18 A, 00-716 Warszawa, Poland (presently Institute of Geological Sciences, PAS. ul. Twarda 51/55, 00-818 Warszawa, Poland). 4Copernicus Science Centre, ul. Wybrzeże Kościuszkowskie 20, 00-390 Warszawa, Poland, 5Łukasiewicz Research Network - Institute of Aviation, Al. Krakowska 110/114, 02-256 Warszawa, Poland. Introduction: We consider a small region in Chryse The material ejected by the explosion covered the valley Planitia ( ~38o14′ N, ~319o25’ E) where several chains and the slopes of the neighboring hills. (iii) Later, the of cones are found – Fig. 1. The cones height are ~10- lower structures (including the valley floor) were 20 m. The considered region is at the boundary of covered with fine aeolian sediments. smooth plain on west (AHcs) and complex unit (AHcc) To test this hypothesis, we computed the apparent on east. The small region (HNck) in north-west corner thermal inertia in this area. is the “older knobby material” – [1], where AH means Amazonian-Hesperian, and HN - Hesperian-Noachian. The region is covered by lacustrine deposits. Note also possible lava flows (in HNck). Small cones are common on Mars. Many cones form chains several kilometers in length.. The mechanisms of their formation are not explained, nor processes responsible for their arrangement in chains. Fig. 1 The region considered in the abstract. The The main subject of our research is the chain of chains of cones are indicated by black arrows and cones labeled 7 in Fig. 1. This chain is in a valley. numbers. Here we suggest that the chain 7 may be a Mechanism of cones formation: Generally there chain of rootless cones formed at the bottom of the are 3 mechanisms of these cones formation: (i) a grains’ valley. NASA. ejection, (ii) from mud or fluidized sand and (iii) explosive formation. Of course, the cones may be formed by several processes. A rootless cone, known also as a pseudocrater, is a volcanic landform which resembles a true volcano but without vent from which lava could have erupted. Rootless cones are formed by steam explosions as a result of flow of hot lava over a wet surface, such as a Fig. 2. ATI along chain 7 (see Fig. 1), calculated from permafrost or a swamp. The hot steam could break the THEMIS thermal bands and CTX based albedo. through the lava layer eventually forming a cone from Dark blue - low values, green-yellow - high values). The tephra like a real volcanic phreatic eruption. low values of ATI in the bottom of valley are probably Our hypothesis: The chain 7 under consideration is a result of later fine aeolian deposits. The high values on located in a valley between two hills. The area west of the both sides the valley indicate larger grains on the the hills is higher than the area to the east. Therefore we surface. suppose that the valley was formed by the flow of water (from west to east) during one of the flash floods. These Thermal inertia (TI or I): I describes reaction of the floods were related to the emergence of large outflow temperature of the planetary surface to the changes of channels. insolation. The thermal inertia unit (in SI) is defined as: The considered chain of cones follows the course of 1 tiu = 1 J m-2 K-1 s-1/2. I is defined as: the valley quite well. Therefore, it is difficult to expect that the cones in the valley are cones of igneous I =(k ρ c)1/2, (1) volcanism. Our hypothesis predicts that: (i) the regolith at the where k is the thermal conductivity [W m-1 K-1], ρ is the valley floor contained significant amounts of water left density, and c is the specific heat capacity. over from the floods. (ii) In the next stage, there was an Apparent Thermal Inertia - data: Apparent overflow of lava in the vicinity of the area currently Thermal Inertia (ATI) approximates the thermal inertia covered by "old knobby material" (HNck). This lava and is based on remote sensing data. Therefore it is used flowed into the valley creating a series of rootless cones. 52nd Lunar and Planetary Science Conference 2021 (LPI Contrib. No. 2548) 2740.pdf in planetary studies. The fundamental equation used for ATI calculation is: ATI=(1-A)/∆T, (2) where ATI is in cgs unit (i.e., in: cal cm-2 K-1 s-1/2 = 4.1855 104 tiu), ΔT is the diurnal temperature difference (in K), and A is the Lambertian albedo (dimensionless). Interpretation: the value of I for non-indurated regolith is mainly controlled by the grain diameter d, i.e. unconsolidated fine material has lower TI than regolith covered by large grains or consolidated rocks. We found that [2]: d=( I2/ (CP0.6 ρc ) ) -1/ (0.11 log(P/K)), (3) where grain diameter d is in μm, ρ is density, c is specific heat, C= 0.0015, K=81000 Torr, P=5 Torr, i.e., average Martian atmospheric pressure (1 Torr = 133.322 Pa). Conclusions and future plans; A comparison of the maps in Figs 1 and 2 shows that the considered chain of cones sequence may be a chain of rootless cones. Accepting another hypothesis poses a number of difficulties. If it were to be igneous cones, then it would be necessary to explain why their chain corresponds exactly to the course of the valley formed by external factors. It is also difficult to accept the hypothesis considered by [2] that these cones were created as a result of the interaction of water in the regolith and the hot igneous intrusion beneath it. In future research we plan to use numerical modeling of cone formation and to consider other chains of cones in similar situations. Acknowledgments: This study was supported by statutory project of Institute of Geophysics of University of Warsaw. We are also grateful to prof. W. Kofman and dr. J. Ciążela for their remarks. References [1] Rotto, S., Tanaka, K. L. (1995) Geologic/ geomorphologic map of the Chryse Planitia: region of Mars. USGS. [2] Czechowski L., et al. (2020), Cones chains in Chryse Planitia and some thermodynamic aspects of their formations. submitted. .